1. Field
Embodiments relate to a compound for an optoelectronic device, an organic light emitting diode including the same, and a display including the organic light emitting diode.
2. Description of the Related Art
An organic optoelectronic device is, in a broad sense, a device for transforming photo-energy to electrical energy or, conversely, a device for transforming electrical energy to photo-energy. As examples, organic optoelectronic devices may include an organic light emitting diode (OLED), a solar cell, a transistor, and the like. An organic light emitting diode has recently drawn attention due to the increase in demand for flat panel displays.
When current is applied to an organic light emitting diode, holes are injected from an anode and electrons are injected from a cathode. Then, injected holes and electrons move to a respective hole transport layer (HTL) and electron transport layer (ETL) and recombine to form a light emitting exciton in an emission layer. The light emitting excitons generate light while shifting to a ground state. The light emission material may be classified as a fluorescent material (using singlet excitons) and a phosphorescent material (using triplet excitons) according to light emitting mechanism. The fluorescent and phosphorescent materials may be used for a light emitting source of an organic light emitting diode.
When electrons are transported from the ground state to the exited state, a singlet exciton may undergo non-light emitting transition to a triplet exciton through intersystem crossing, and the triplet exciton may be transited to the ground state to emit light. Such light emission is referred to as phosphorescent emission. When the triplet exciton is transited, it may not directly transit to the ground state. Therefore, it may be transited to the ground state after the electron spin is flipped. Accordingly, a half-life (light emitting time, lifetime) of phosphorescent emission is longer than that of fluorescent emission.
When holes and electrons are recombined to produce a light emitting exciton, three times as many triplet light emitting excitons may be produced, compared to the amount of the singlet light emitting excitons. A fluorescent material has 25% of the singlet-exited state and a limit in luminous efficiency. On the other hand, a phosphorescent material may utilize 75% of the triplet exited state and 25% of the singlet exited state, so it may theoretically reach 100% of the internal quantum efficiency. Accordingly, the phosphorescent light emitting material may have advantages of accomplishing around four times greater luminous efficiency than the fluorescent light emitting material.